Rotary valves are widely used in the process industries for directing fluids from one or more process sources to one or more process destinations in repeatable cyclic process steps. These valves, also called rotary sequencing valves, are used in cyclic or repeatable processes such as gas separation by pressure or temperature swing adsorption, liquid separation by concentration swing adsorption, gas or liquid chromatography, regenerative catalytic processes, pneumatic or hydraulic sequential control systems, and other cyclic processes.
One type of rotary valve has a cylindrical configuration in which inner or outer cylinders with properly positioned ports and seals rotate relative to one another such that ports in the inner and outer cylinders are aligned and/or blocked in a predetermined cyclic sequence. Another type of rotary valve has a flat circular configuration in which a flat ported rotor rotates coaxially on a flat ported stator such that ports in the stator and rotor are aligned or blocked in a predetermined cyclic sequence. Sealing typically is provided by direct contact of the flat rotor face sliding over the flat stator face. A high degree of precision is required in the fabrication of these flat surfaces to prevent excessive leakage at the mating surfaces. Rigid materials such as metal, carbon, or ceramic typically are used for rotors and stators, and wear of the parts or distortions caused by temperature differentials will cause changes in the shape of the surfaces, thereby allowing leakage across the seal formed between the surfaces. A sheet of deformable material may be bonded to the rotor or stator face to improve the seal between the rotor and stator.
Rotary circular valves with a flat circular configuration are particularly useful in pressure swing adsorption systems utilizing multiple parallel adsorber beds operating in overlapping cyclic steps which include feed, pressure equalization, depressurization, purge, and repressurization steps. As the size and throughput of an adsorption system increases, the diameters of the circular rotary valves also increase. As these valves increase in diameter, typically above about six inches, it becomes increasingly expensive to machine rotor and stator surfaces with the high degree of flatness required for proper fluid sealing between the rotor and stator faces. In addition, larger valve sizes magnify the problem of deviations from flatness caused by wear between the surfaces, thermal distortion of the mating parts, internal manufacturing stresses, or stresses from the pressure of the fluid flowing through the valve.
These problems are addressed by embodiments of the present invention, as described below and defined by the claims which follow, providing an improved rotary valve that alleviates sealing problems caused by flatness deviations due to rotor and stator fabrication, and also compensates for wear and thermal distortion during valve operation.